Abstract
Molting, that is, the synthesis and shedding of a cuticular exoskeleton, is a defining characteristic of ecdysozoa. In nematodes such as C. elegans, molts rhythmically terminate each of four larval stages. The molting cycle is tightly coupled to the rhythmic expression of thousands of genes. The mechanisms that support the regular molting cycle and oscillatory gene expression have remained largely elusive. Here, we performed an RNAi-based screen for transcription factors required for molting to identify potential components of a molting clock. We find that depletion of GRH-1, BLMP-1, NHR-23, NHR-25, MYRF-1 or BED-3 impairs progression through the molting cycle. We characterize GRH-1, a Grainyhead/LSF transcription factor whose functions in C. elegans development have remained largely unexplored, but whose orthologues in other animals are known to be key epithelial cell fate regulators. We show that GRH-1 depletion causes a dose-dependent extension of molt duration, with severe depletion causing defects in cuticle formation and shedding, and larval death. GRH-1 is required repetitively, during a specific time window prior to each larval molt. This rhythmic activity is consistent with the rhythmic accumulation of GRH-1 protein. These features are consistent with GRH-1 functioning as a key component, or high-level output, of the a gene regulatory network that controls molting. As its mammalian orthologues, as well as those of BLMP-1 and NHR-23, have been implicated in rhythmic homeostatic skin regeneration in mouse, the mechanisms underlying rhythmic C. elegans molting may be conserved beyond nematodes.
Competing Interest Statement
The authors have declared no competing interest.
